Log periodic antenna with parasitic elements interspersed in log periodic manner



1966 N. BARBANO 3,286,268

LOG PERIODIC ANTENNA WITH PARASITIG ELEMENTS INTERSPERSED IN LOG PERIODIC MANNER Filed Jan. 2, 1964 5 Sheets-Sheet l INVENTOR. NORMAND BARBANO ATTO R NEY Nov. 15, 1966 N BARBANO 3,286,268

LOG PERIODIC ANTE NNA WITH PARASITIC ELEMENTS INTERSPERSED IN LOG PERIODIC MANNER Filed Jan. 2,, 1964 5 Sheets-Sheet 2 24 INVENTOR.

NORMAND BARBANO ATTORNEY Nov. 15, 1966 N. BARBANO 3,286,268

LOG PERIODIC ANTENNA WITH PARASITIC ELEMENTS INTERSPERSED IN LOG PERIODIC MANNER Filed Jan. 2, 1964 5 Sheets-Sheet :5

I I3 'Ei INVENTOR Nov. 15, 1966 N. BARBANO LOG PERIODIC ANTENNA WITH PARASITIC ELEMENTS INTERSPERSED IN LOG PERIODIC MANNER' Filed Jan. 2, 1954 5 Sheets-Sheet 4 I 0 3 N H m w I M w fi i m x z .u r n e a n c I x I M ATTO R N EY Nov. 15, 1966 BARBANO 3,

LOG PERIODIC AN NA WITH PARAS TS I D ITIG ELEMEN INTERSPERSED IN LOG PER 0 IC MANNER Filed Jan. 3, 1964 5,Sheets-Sheet 5 NORMAND BARBANO BY (/ZwXM/L TTO RNEX United States Patent 3,286,268 LOG PERIODIC ANTENNA WITH PARASITIC ELE- MENTS INTERSPERSED IN LOG PERIODIC MANNER Normand Barbano, Sunnyvale, Calif., assignor to Sylvania Electric Products Inc., a corporation of Delaware Filed Jan. 2, 1964, Ser. No. 335,001 6 Claims. (Cl. 343-792.5)

This invention relates to broadband antennas and more particularly to improved log periodic dipole and monopole antenna arrays.

Log periodic antennas have the desirable characteristics of maintaining a relatively constant radiation pattern and impedance over indefinitely large bandwidths. The dipole antenna is one of the most basic and commonly employed antennas because of its simplicity of design, construction and operation. The log periodic dipole antenna array is basically a relatively simple antenna comprised of a plurality of center fed dipole antennas centered about a reference axis. The lengths of the dipoles and the spacing between axially adjacent dipoles increase from one end of the array to the other. In order that the log periodic dipole antenna array operates independently of frequency it is necessary to shift the phase of an applied electromagnetic signal 180 degrees between adjacent dipoles. The conventional method of obtaining this phase reversal, by mechanically twisting a twin lead feed line 180 degrees between its connection to adjacent dipoles, does not provide an antenna that is mechanically and electrically symmetrical about the reference axis. Thus, this log periodic dipole antenna array does not have a corresponding log periodic monopole antenna array. Other more complicated antenna feed mechanisms are employed to feed the log periodic monopole antenna array.

An object of this invention is the provision of a log periodic dipole antenna array that is mechanically and electrically symmetrical about a reference axis.

Another object is the provision of an improved log periodic dipole antenna array having a corresponding log periodic monopole antenna array.

Another object is the provision of an improved feed for log periodic dipole and monopole antenna arrays.

Another object is the provision of improved log periodic dipole and monopole antenna arrays that are relatively simple to construct.

Another object is the provision of a log periodic antenna having increased directivity.

Another object is the provision of a log periodic antenna having an increased front to back ratio.

In accordance with this invention the log periodic dipole antenna array is symmetrical about a reference axis. The antenna comprises a plurality of parallel conductive elements centered about the reference axis. In the preferred embodiment, the lengths of and the spacing between the conductive elements increases logarithmically from one end of the antenna to the other. Alternate conductive elements are dipoles which are center fed by a two conductor antenna feed and are thus driven elements. The half of each dipole on one side of the reference axis is connected to one conductor of the antenna feed. The other conductor of the feed is connected to the half of the driven element on the other side of the reference axis. The other alternate conductive elements are electrically isolated from the antenna feed and are thus parasitic elements.

The corresponding log periodic monopole antenna array is a relatively simple structure which comprises onehalf of the symmetrical log periodic dipole antenna array, for example the half above the reference axis, mounted over a conductive ground plane. One conductor of the antenna feed is insulated from the ground plane and is "ice directly electrically connected to the driven elements. The other conductor of the antenna feed is directly electrically connected to the conductive ground plane and to the other alternate conductive elements which are parasitic elements.

This invention and its objects will be more fully understood from the following detailed description thereof, reference being had to the accompanying drawings in which:

FIGURE 1 is a plan view of a dipole antenna array, partly in section, embodying this invention;

FIGURE 2 is a section taken on the line 22 of FIG- URE 1;

FIGURE 3 is a modified form of the antenna array of FIGURE 1;

FIGURE 4 is the monopole antenna array corresponding to the dipole antenna array of FIGURE 1;

FIGURE 5 is a section taken on line 55 of FIG- URE 4;

FIGURE 6 is a monopole antenna array corresponding to the dipole antenna array of FIGURE 3; and

FIGURES 7-9, inclusive, are radiation patterns of a monopole antenna array similar to that of FIGURE 4.

Reference being had to FIGURE 1, the log periodic dipole antenna array 10 comprises a non-conducting plane sheet 11 with a central axis 00 and having a plurality of axially spaced center fed dipole elements 12 on one side 11' of sheet 11 and a number of single axially spaced conductor elements 14 on the other side 11" of the sheet. Each dipole 12 consists of a pair of conductive arms 12A and 12B of the same length on opposite sides of axis 00. The arms are symmetrical about and equally spaced from the axis. The arms extend in a direction transverse to and are preferably perpendicular to the axis. Each single conductive element 14 is preferably associated with an adjacent dipole 12 on the opposite side of the sheet as shown in FIGURE 1. The single conductive elements 14 are symmetrically disposed about axis 00 and are preferably parallel to the dipoles 12. The lengths of the dipole and single elements and the axial spacing between adjacent elements are progressively larger in one axial direction, right to left as reviewed in FIGURE 1.

Conductors 16 and 17 extend on side 11 of sheet 11 parallel to and on opposite sides of axis 00 for substan tially the length of the sheet. Conductor 16 is electrically connected to the inner end of each dipole arm 12A. Conductor 17 is similarly connected to the inner end of each dipole arm 12B. Single elements 14 by their location on the opposite side 11" of the sheet are electrically insulated from the conductors 16 and 17.

Dipoles 12, single elements 14 and conductors 16 and 17 preferably are formed on insulator sheet 11 by wellknown printed circuit techniques and may comprise copper or similar conducting metal.

The array is electrically coupled to associated circuits by a coaxial line 20 having an outer conductor 21-and an inner conductor 22. Line 20, electrically connected to a circuit 24 which may be a receiver or transmitter, extends in juxtaposition with conductor 17 toward the converging end of the array. Outer conductor 21 of the coaxial line is electrically connected to the conductor 17 and terminates at the convergent end of the array. The inner conductor 22 extends beyond the outer conductor 21 and is electrically connected at 25 to a conducting rod 26 which extends alongside and is electrically connected to conductor 16. The connection'at 25 is called the feed point of the array, i.e., the point from which a balanced feed of the array appears to occur.

The outer ends of dipoles 12 and of single elements 14 lie in converging planes which intersect in a line 27 spaced ahead of (to the right in FIGURE '1) the convergent end of the array. The lengths of the arms 12A and the element spacing to element length ratio 122i 2 tang where /T is a constant having a value less than one, I is the length of the n conductive element from 27, l n+1 is the length of the adjacent longer element, x is the distance from 27 to the conductive element I x(n+1) is the corresponding distance to the conductive element l and S is the spacing between the conductive element I and the adjacent shorter conductive element.

The log periodic antenna is noted for its frequency independent operation, for having a relatively constant beamwidth and input impedance, when operated over an extremely-broad band of frequencies. The active region of the antenna occurs where the electrical length of an element is nearly a half-wavelength long. A number of elements of a log periodic dipole antenna array are simultaneously active or pseudo-resonant so that the apparent phase center of the antenna beam will progress smoothly between elements as the operating frequency is changed.

It is necessary in a log periodic dipole antenna array to shift the phase of an applied electromagnetic signal 180 degrees between adjacent conductive elements (i.e., 1214, 1412, etc.) in order to obtain frequency independent operation. This phase reversal is facilitated by the novel and symmetrical feed of this invention and is accomplished by the single conductive elements 14 which are physically separated and electrically isolated from the conductive dipole arms 12A and 12B, coaxial line 20 and conductive rod 26', as illustrated in FIG- URE 2. The single conductive elements 14 are physically parasitic elements. I The parasitic elements 14 in the embodiment of FIG- URE 1 are located in the position of alternate driven elements of a conventional log periodic dipole antenna array and perform the function of the driven elements they replace. The parasitic elements are excited through mutual coupling between adjacent elements. An applied signal is shifted 180 degrees in phase when it is coupled to the parasitic clement. There is no noticeable difference in antenna operation when a parasitic element and an adjacent driven element are individually loaded. It has been determined empirically that the apparent phase center of an applied signal progresses continuously and smoothly from a driven element to an adjacent parasitic element and then to the next driven element. As the parasitic element acts as an equivalent source and radiates energy as does the driven element it replaces, it is etfectively a driven element.

A modified form of the invention, for providing a log periodic antenna having increased directivity and frontto-back ratio, is illustrated in FIGURE 3. Like reference characters refer to like elements in the drawings. The antenna comprises a group of parasitic elements, such as the parasitic elements 14B and 14F between adjacent driven elements, such as 12 and 12'. The parasitic elements are preferably the same length as the corresponding parasitic element they replace in the antenna of FIGURE 1. For an antenna having a -r of 0.9

and an or. of 14.25 degrees, the parasitic elements 14E and 14F are preferably located from the adjacent shorter driven element approximately 43 and 68% respectively, of the distance between adjacent driven elements 12.

The log periodic dipole antenna array 10 of FIG- URE 1 has a corresponding log periodic monopole array 30, which is illustrated in FIGURE 4, since the conductive elements and the antenna feed are symmetrical about the axis 0-0. The log periodic monopole antenna array 30 essentially comprises the upper half of the dipole antenna 10 mounted on and perpendicular to a ground plane 31. The conductive arms 12A are each electrically connected to the conductive strip 26 as in the embodiment of FIGURE 1.

The ground plane 31 preferably comprises a nonconductive plane sheet 34 having a thin sheet 35 of conductive material, such as copper, secured to one side. The coaxial transmission line 20 is secured to the nonconductive side 36 of sheet 34. The outer conductor 21 of the coaxial line is extended through an opening 37 in the ground plane and is electrically connected at 38 (see FIGURE 5) to the ground plane conductive sheet 35. One end of each single conductive element 14' is connected to the ground plane conductive sheet 35, for example by solder, as indicated at 14C. The center conductor 22 of the coaxial line is extended beyond outer conductor 21 at the opening 37 and electrically connected through conductive rod 26 to conductive strip 16 and the single conductive elements 14.

The log periodic monopole antenna array 30' (see FIGURE 6) employs a pair of parasitic elements E and F between adjacent driven elements 12. The parasitic elements are electrically connected to ground plane conductive sheet 35 and to the outer conductor 21 of the coaxial transmission line as in the embodiment of FIG- URE 4.

By way of example, a log periodic monopole antenna array of the type shown in FIGURE 4 and having the following dimensions and operating characteristics was built and successfully operated:

7' 0.898 oc/Z degrees 25 s/l 0.0559 Number of driven elements 21 Number of parasitic elements 21 Conductive element material copper Shortest driven element:

The operation of this antenna is shown in part in FIGURES 7-9. The operating bandwidth may be extended by increasing the number of conducting elements. The E-plane patterns correspond to vertical cut in the radiation pattern in which the electrical polarization vector is orthogonal to the ground plane. The H-plane patterns are taken in a plane orthogonal to the E-plane and inclined 20 degrees to the ground plane. The ground plane intersects the E-plane patterns at Zero degrees. These patterns show a well formed beam of about 38 degrees half-power beam width in the E-plane and degrees beamwidth in the H-plane. This corresponds to about 8db directive gain above that of an isotropic radiator. Gain and pattern shape are almost constant over the entire frequency range. The beam is symmetric in the H-plane, and in the E-plane is inclined about 20-30 degrees to the ground plane.

Changes, improvements and modifications of the abovedescribed embodiments of this invention may be made by those skilled in the art without departing from the precepts and spirit of the invention, the scope of which is de-- fined in the appended claims.

What is claimed is:

1. A log periodic antenna with an axis, said antenna comprising a plurality of parallel axially spaced conducting elements extending in directions transverse to said axis,

the linear dimensions and axial spacings of successive ones of said elements increasing in a direction from one end of the antenna to the other such as that lines through the opposed extremities of said elements intersect,

said elements consisting of first and second sets of elements,

the elements of the first set axially alternating with elements of the second set,

a pair of conductors for coupling electromagnetic wave energy between said elements and associated circuits,

said conductors being symmetrically disposed about and parallel to said axis, and

said first set of elements comprising a plurality of pairs of elements, the elements of each of said pairs being on opposite sides of said axis and being directly electrically conected at their proximate ends to said conductors, respectively,

the second set of elements traversing said axis and being electrically insulated from said conductors.

2. A broadband antenna comprising a planar sheet of insulator material having a longitudinal axis,

a first set of conductive elements on one side of said sheet comprising a plurality of pairs of arms with the arms of each pair being on opposite sides of the axis and being of equal length,

a second set of conductive elements on the other side of said sheet and axially arranged such that alternate conductive elements are of the same set,

the conductive elements of said first and second sets being substantially parallel and being normal to said axis,

the lengths and spacings of conductive elements increasing in a direction from one end of the antenna to the other such that lines through the outer ends of the element intersect to form an acute angle,

a first conductive strip on said one side of said insulator sheet substantially parallel to said axis,

means for electrically connecting said first conductive strip to the arms on the one side of the axis,

a second conductive strip on said one side of said insulator sheet and on the other side of and substantially parallel to the axis,

means for electrically connecting said second conductive strip to the arms on the other side of the axis, and

a coaxial transmission line antenna feed comprising an outer conductor electrically connected to said first conductive strip, and 1 an inner conductor electrically connected to said second conductive strip.

3. The combination of an antenna array having an axis and a ground plane, said array comprising a plurality of parallel axially spaced conducting elements projecting away from said ground plane,

the linear dimensions and axial spacings of successive ones of said elements increasing in a direction from one end of the antenna to the other,

a two-conductor transmission line for coupling electromagnetic wave energy between said elements and associated circuits,

one of said conductors being electrically connected to said ground plane, and

the other of said conductors extending the full length of the antenna, and

said plurality of elements consisting of first and second sets of elements,

the elements of the first set axially alternating with elements of the second set and being directly electrically connected at their ends proximate to the aXis to said other conductor, and the elements of the second set being directly electrically connected to said ground plane and being insulated from said other conductor. 4. A log periodic antenna having an axis and an end fire pattern extending in a given direction comprising an antenna feed comprising a pair of conductors, a plurality of radiating elements directly electrically connected to at least one of said conductors and extending in a direction transverse to said axis with the ends thereof remote from said connection aligned in a straight line which converges toward the axis, all of said radiating elements which are on one side of the axis being connected to the same one of said conductors, and a plurality of parasitic elements, at least one of said parasitic elements being located between each pair of adjacent radiating elements, the axial spacing of successive ones of all of said radiating and parasitic elements increasing in the direction from the point of convergence to the opposite end of the antenna according to the relationship where qis a constant having a value less than 1, x is the distance from the point of convergence to the n element, and x is the corresponding distance from the point of convergence to the n+1 element. 5. The antenna array according to claim 4 in which one end of each of said parasitic elements is aligned with said ends of said radiating elements along the converging straight line.

6. A broadband antenna having an axis comprising a plurality of center fed conductive dipole elements arranged in a row symmetrically about said axis,

the length and spacing of said dipole elements increasing in a direction from one end of the row to the other such that lines through the dipole element extremities intersect,

a plurality of conductive parasitic elements symmetrically arranged about the axis in a row with two of said parasitic elements between adjacent dipole elements,

one of said parasitic elements being located substantially 43% of the distance between adjacent dipole elements as measured from the shorter adjacent dipole element,

the other of said parasitic elements being located substantially 68% of the distance between adjacent dipole elements as measured from the shorter adjacent dipole element, and

an antenna feed comprising a first conductor electrically connected to the dipole elements on one side of the axis, and

a second conductor electrically connected to the dipole elements on the other side of the axis.

References Cited by the Examiner UNITED STATES PATENTS Re. 25,604 6/ 1964 Greenberg 343--792.5 X 2,716,703 8/1955 Kane 343-815 X 3,082,422 3/1963 Watkins 343-814 3,092,835 6/1963 Jaytanie 34381S X 3,113,316 12/1963 Berry 343-792.5 3,123,827 3/1964 Arnold et al. 343792.5

HERMAN KARL SAALBACH, Primary Examiner.

R. F. HUNT, JR., Assistant Examiner. 

4. A LOG PERIODIC ANTENNA HAVING AN AXIS AND AN END FIRE PATTERN EXTENDING IN A GIVEN DIRECTION COMPRISING AN ANTENNA FEED COMPRISING A PAIR OF CONDUCTORS, A PLURALITY OF RADIATING ELEMENTS DIRECTLY ELECTRICALLY CONNECTED TO AT LEAST ONE OF SAID CONDUCTORS AND EXTENDING IN A DIRECTION TRANSVERSE TO SAID AXIS WITH THE ENDS THEREOF REMOTE FROM SAID CONNECTION ALIGNED IN A STRAIGHT LINE WHICH CONVERGES TOWARD THE AXIS, ALL OF SAID RADIATING ELEMENTS WHICH ARE ON ONE SIDE OF THE AXIS BEING CONNECTED TO THE SAME ONE OF SAID CONDUCTORS, AND A PLURALITY OF PARASITIC ELEMENTS, AT LEAST ONE OF SAID PARASITIC ELEMENTS BEING LOCATED BETWEEN SAID PAIR OF ADJACENT RADIATING ELEMENTS, THE AXIAL SPACING OF SUCCESSIVE ONES OF ALL OF SAID RADIATING AND PARASITIC ELEMENTS INCREASING IN THE DIRECTION FROM THE POINT OF CONVERGENCE TO THE OPPOSITE END OF THE ANTENNA ACCORDING TO THE RELATIONSHIP 